Decline In Primary Production Research Articles

Global Challenges Facing Plant Pathology: A Review on Multidisciplinary Approaches to Meet the Food Security

Plant disease outbreaks cause a decline in primary productivity and biodiversity, which negatively impacts the socioeconomic and environmental circumstances in the afflicted areas. They also pose significant threats to the environment's sustainability and the world's food security. Climate change increases the risk of outbreaks by altering host-pathogen interactions, altering the development of pathogens, and encouraging the emergence of new pathogenic strains. Changes in the range of pathogens can cause plant diseases to spread more quickly in new areas. In this review, we examine the potential effects of future climatic scenarios on plant disease pressures and the resulting effects on plant productivity in agricultural and wild environments. We study the effects of climate change, both now and in the future, on disease incidence and severity, pathogen biogeography, natural ecosystems, agriculture, and food production. To mitigate future disease outbreaks, we propose modifying the current conceptual framework and integrating eco-evolutionary theories into studies to improve our mechanistic comprehension and prediction of pathogen spread in future climates. We stress the need of an interface between science and policy that works closely with relevant intergovernmental organisations to provide effective monitoring and management of plant disease under future climate scenarios. This will be necessary to ensure long-term food and nutrient security as well as the sustainability of natural ecosystems.

Climate change impacts on small pelagic fish distribution in Northwest Africa: trends, shifts, and risk for food security

Climate change is recognised to lead to spatial shifts in the distribution of small pelagic fish, likely by altering their environmental optima. Fish supply along the Northwest African coast is significant at both socio-economic and cultural levels. Evaluating the impacts of climatic change on small pelagic fish is a challenge and of serious concern in the context of shared stock management. Evaluating the impact of climate change on the distribution of small pelagic fish, a trend analysis was conducted using data from 2363 trawl samplings and 170,000 km of acoustics sea surveys. Strong warming is reported across the Southern Canary Current Large Marine Ecosystem (CCLME), extending from Morocco to Senegal. Over 34 years, several trends emerged, with the southern CCLME experiencing increases in both wind speed and upwelling intensity, particularly where the coastal upwelling was already the strongest. Despite upwelling-induced cooling mechanisms, sea surface temperature (SST) increased in most areas, indicating the complex interplay of climatic-related stressors in shaping the marine ecosystem. Concomitant northward shifts in the distribution of small pelagic species were attributed to long-term warming trends in SST and a decrease in marine productivity in the south. The abundance of Sardinella aurita, the most abundant species along the coast, has increased in the subtropics and fallen in the intertropical region. Spatial shifts in biomass were observed for other exploited small pelagic species, similar to those recorded for surface isotherms. An intensification in upwelling intensity within the northern and central regions of the system is documented without a change in marine primary productivity. In contrast, upwelling intensity is stable in the southern region, while there is a decline in primary productivity. These environmental differences affected several small pelagic species across national boundaries. This adds a new threat to these recently overexploited fish stocks, making sustainable management more difficult. Such changes must motivate common regional policy considerations for food security and sovereignty in all West African countries sharing the same stocks.

Productivity of Spitsbergen fjords ecosystems in summer-Spatial changes of insitu primary production in Kongsfjorden and Hornsund in the period 1994-2019.

This comprehensive study examines primary production (PP) within the Spitsbergen fjords, Hornsund, and Kongsfjord, over a 25-year period (1994-2019), across 45 stations and 348 incubation levels at various depths. PP and hydrological parameters were measured at 28 sampling stations in Kongsfjorden and 17 in Hornsund, with the locations of "Glacier," "Inner," and "Outer" zones defined to reflect the varying influence of glacial meltwater. Our study revealed spatial and temporal variability in PP, both at the surface and within the water column with very high depth resolution. The highest PP values were observed in the Glacier and Inner zones of Hornsund, particularly in the water layer up to 3 m depth, exceeding 20 mgC m-3 h-1. A notable decline in PP with increasing depth was observed in both fjords, with the Glacier zones displaying the highest productivity at the surface. The study also highlights the influence of glacial meltwater on surface water conditions, affecting the PP in the upper layers of both fjords. The observed gradient in the depth of maximum PP toward the mouth of the fjord varied between the two fjords, with Kongsjord displaying more dynamic variations. The spatial distribution of integrated primary production (Pi) suggested lower productivity in the glacial regions, likely due to light limitation caused by high concentrations of mineral particulate matter. The values of Pi were considerably higher in Hornsund, approximately twice as high overall, with specific emphasis on the Glacier and Inner zones where Pi values were about 6.5 and 2.5 times higher, respectively, when compared to those observed in Kongsfjord.

Influence of circulation processes on cyanobacteria bloom and phytoplankton succession in the Baltic Sea coastal area

Many studies related to the influence of eddies on the primary production chain of marine ecosystems have been conducted; however, this effect tends to be regionally specific, especially in coastal dynamic waters. In the Baltic Sea, mesoscale and submesoscale eddies are a ubiquitous feature of water circulation during summer, when diazotrophic cyanobacteria blooms occur in surface waters due to the excess of phosphorus in seawater. Climatic change may increase the frequency and duration of these negative events in the marine ecosystem. We examined the taxonomic composition, abundance, and primary production of phytoplankton in the southeastern Baltic Sea during the occurrence of the packed eddy system at the end of the abnormally warm summer of 2018. Massive cyanobacteria growth was observed in the plume of the eutrophic Vistula Lagoon in the Gulf of Gdansk. The only species diazotrophic Dolichospermum flos-aquae ((Bornet & Flahault) P. Wacklin, L. Hoffmann & Komárek, 2009) vegetated along the western coast of the Sambia Peninsula. Its colonies reached the highest biomass nearby the dumping site of the Amber Mining Plant in Yantarny, Kaliningrad Region, Russia. The cyanobacteria colonies dispersed in the outgoing jet of a relatively warm eddy dipole. Chrysochromulina spp. (Lackey, 1939) was dominant in these nitrogen-rich waters. In contrast, cryptophyte species dominated in the relatively cold waters of the dipole anticyclone that resulted in a fourfold decline in primary production. The decrease in the number of mobile phytoplankton species was revealed within the “old” eddies near the northern coast of the Sambia Peninsula and the Curonian Spit. Meanwhile, species of the spring–autumn complex Coscinodiscus granii (Gough, 1905), Peridiniella catenate ((Levander) Balech, 1977) and other developed in the community. This implies that the appearance of eddies can cause phytoplankton succession in the coastal area. The mechanism of their influence was similar to the action of other physical factors perturbing a relatively stationary environment. Capture of cyanobacterial colonies by eddies led to an improvement of the ecological situation in the area, as cyanobacteria transported their biomass outside the coastal area. However, the opposite direction processes obviously were the deterioration of light conditions, increased water turbidity, and organic matter concentration.

Retrospective analysis of the pelagic ecosystem of the Western Mediterranean Sea: Drivers, changes and effects

In the Western Mediterranean Sea, forage fishes have changed in abundance, body condition, growth, reproduction, and distribution in the last decades. Different hypotheses have been proposed to explain these changes, including increase in fishing mortality; changes in environmental conditions affecting species fitness, and planktonic productivity and quality; recovery of top predators; and increase in competitors. We investigated the main drivers and changes of the pelagic ecosystem and their effects using an ecosystem-based modelling approach. Specifically, we (1) quantified the potential historical contribution of various drivers of change, (2) investigated changes in temporal trends and spatial distributions of main ecosystem components, and (3) identified ecological consequences of these changes in top predator and competitors, their fisheries and ecosystem traits during 2000–2020. We updated an established Ecopath food-web model representing the Spanish and French Mediterranean sub-areas (GSA06 and GSA07) in 2000 with recent available data. We applied the temporal dynamic Ecosim module, and tested historical time series of fishing effort, fishing mortality and environmental factors as potential drivers. Observed biomass and landings of key species were used to validate model projections. A spatial-temporal Ecospace model was developed to project species distribution changes. Results showed historical biomass and catch changes driven by a combination of high fishing pressure and environmental change (i.e. increase in temperature and salinity, and decline in primary productivity). Small pelagic fish showed significant temporal changes and predicted shifts in their distributions, following a latitudinal gradient. Predators and competitors showed changes as well, displaying heterogeneous spatial patterns, while fisheries landings declined. Overall, results matched observations (e.g., decline of sardine, fluctuations of anchovy and increases in bluefin tuna) and illustrated the need to complement traditional assessments with integrative frameworks to move towards an ecosystem-based approach in the Mediterranean. They also highlighted important knowledge gaps to guide future research in the region.

Trophic amplification: A model intercomparison of climate driven changes in marine food webs.

Marine animal biomass is expected to decrease in the 21st century due to climate driven changes in ocean environmental conditions. Previous studies suggest that the magnitude of the decline in primary production on apex predators could be amplified through the trophodynamics of marine food webs, leading to larger decreases in the biomass of predators relative to the decrease in primary production, a mechanism called trophic amplification. We compared relative changes in producer and consumer biomass or production in the global ocean to assess the extent of trophic amplification. We used simulations from nine marine ecosystem models (MEMs) from the Fisheries and Marine Ecosystem Models Intercomparison Project forced by two Earth System Models under the high greenhouse gas emissions Shared Socioeconomic Pathways (SSP5-8.5) and a scenario of no fishing. Globally, total consumer biomass is projected to decrease by 16.7 ± 9.5% more than net primary production (NPP) by 2090-2099 relative to 1995-2014, with substantial variations among MEMs and regions. Total consumer biomass is projected to decrease almost everywhere in the ocean (80% of the world's oceans) in the model ensemble. In 40% of the world's oceans, consumer biomass was projected to decrease more than NPP. Additionally, in another 36% of the world's oceans consumer biomass is expected to decrease even as projected NPP increases. By analysing the biomass response within food webs in available MEMs, we found that model parameters and structures contributed to more complex responses than a consistent amplification of climate impacts of higher trophic levels. Our study provides additional insights into the ecological mechanisms that will impact marine ecosystems, thereby informing model and scenario development.

Positive and negative effects of marine transgression on the quality of lacustrine source rocks in the Upper Cretaceous Songliao Basin, China

The linkage between marine transgression and lacustrine source rock development has been highlighted for decades. Here, improved understandings were obtained on this challenging issue based on valuable comprehensive profiles from the Upper Cretaceous Songliao Basin, NE China (Qingshankou Formation, brief as K2qn1). 48 shale samples from the Central Depression in the northern Songliao Basin were analysed to establish three geochemical profiles of K2qn1. Multiple biomarkers suggested that organic matter in the source rocks of K2qn1 was mainly sourced from aquatic organisms. Systematic organic and inorganic geochemical analyses reveal that at least five transgressive events occurred during the sedimentary period of K2qn1, denoted as TI, TII, TIII, TIV, and TV from bottom to top. In the context of multiple transgression events, the quality of K2qn1 source rocks was primarily controlled by lacustrine primary productivity. Importantly, transgression events have both positive and negative effects on the quality of lacustrine source rocks. During earlier transgressive events (e.g., TI and TII), the quality of source rocks was negatively correlated with transgression intensity, which is likely due to the difficulty of freshwater organisms adapting to salinity, resulting in a decline in primary productivity. In the later transgression events (e.g., TIII and Tv), the quality of source rocks was positively correlated with transgression intensity, which is probably due to the gradual dominance of salt-tolerant or halophilic organisms during multiple stages of salinization. This study provides a comprehensive research approach for evaluating the influence of transgression events on lacustrine source rocks.

Restricting electron flow at cytochrome b6f when downstream electron acceptors are severely limited.

Photosynthetic organisms frequently experience abiotic stress that restricts their growth and development. Under such circumstances, most absorbed solar energy cannot be used for CO2 fixation and can cause the photoproduction of reactive oxygen species (ROS) that can damage the photosynthetic reaction centers of PSI and PSII, resulting in a decline in primary productivity. This work describes a biological "switch" in the green alga Chlamydomonas reinhardtii that reversibly restricts photosynthetic electron transport (PET) at the cytochrome b6f (Cyt b6f) complex when the capacity for accepting electrons downstream of PSI is severely limited. We specifically show this restriction in STARCHLESS6 (sta6) mutant cells, which cannot synthesize starch when they are limited for nitrogen (growth inhibition) and subjected to a dark-to-light transition. This restriction represents a form of photosynthetic control that causes diminished electron flow to PSI and thereby prevents PSI photodamage but does not appear to rely on a ΔpH. Furthermore, when electron flow is restricted, the plastid alternative oxidase (PTOX) becomes active, functioning as an electron valve that dissipates some excitation energy absorbed by PSII and allows the formation of a proton motive force (PMF) that would drive some ATP production (potentially sustaining PSII repair and nonphotochemical quenching [NPQ]). The restriction at the Cyt b6f complex can be gradually relieved with continued illumination. This study provides insights into how PET responds to a marked reduction in availability of downstream electron acceptors and the protective mechanisms involved.

Sex-specific digestive performance of mussels exposed to warming and starvation.

As global climate change has dramatically impacted the ocean, severe temperature elevation and a decline in primary productivity has frequently occurred, which has affected the structure of coastal biomes. In this study, the sex-specific responses to temperature change and food availability in mussels were determined in terms of digestive performance. The thick-shelled mussels Mytilus coruscus (male and female) were exposed to different temperature and nutritional conditions for 30 days. The results showed that the digestive enzymes of mussels were significantly affected by temperature, food, sex, and their interactions. High temperature (30°C) and starvation significantly decreased amylase, lysozyme, and pepsase activities of female mussels, while trypsin and trehalase did not change significantly at the experimental end. The activity of amylase, trypsin, and trehalase was significantly reduced in males at high temperature (30°C) under starvation treatment, but high temperature (30°C) elevated pepsase. Unsurprisingly, starvation caused the reduction of lysozyme and pepsase under 25°C in males. Amylase, lipase, and trehalase were higher in female mussels compared with males, while the enzymatic activities of lysozyme, pepsase, and trypsin were higher in male mussels than females. Principal component analysis showed that different enzyme activity indexes were separated in male and female mussels, indicating that male and female mussels exhibited significantly different digestive abilities under temperature and food condition change. The study clarified sex-specific response difference in mussel digestive enzymes under warming and starvation and provided guidance for the development of mussel aquaculture (high temperature management and feeding strategy) under changing marine environments.

Physiological and metabolic effects of glyphosate as the sole P source on a cosmopolitan phytoplankter and biogeochemical implications

Nutrient conditions influence the physiology and stoichiometry of marine phytoplankton. While extensive studies have documented the effects of abundances and types of nutrients such as nitrogen (N) and phosphorus (P), the effect of phosphonates as a P source is less understood and underexplored. Here, with the cosmopolitan coccolithophorid Emiliania huxleyi as a model phytoplankter, we investigated the effect of the phosphonate type of herbicide glyphosate as the sole P source in comparison with the P-depleted and P-replete (with 36 μM dissolved inorganic phosphate [DIP]) cultures. We measured changes in cellular C (carbon):P and N:P ratios and physiological performance and documented the corresponding transcriptomic and miRNAomic responses in E. huxleyi to glyphosate treatment. We found that glyphosate supported population growth but not to the full scale relative to DIP, and this was under the concerted regulation of DNA replication and cell cycle arrest genes as well as the growth-regulating miRNA. Furthermore, our data suggest that E. huxleyi took up glyphosate directly, bypassing extracellular hydrolysis, and this involved ABC transporters. Meanwhile, glyphosate-grown cultures displayed marked increases in cellular particulate organic C (POC) and PON contents, cell size, and transcription of genes for CO2 fixation and citrate cycle, nitrate transport, and protein biosynthesis. However, compared to DIP, the maximum absorption rate of glyphosate was only 33%, and glyphosate-grown E. huxleyi cells exhibited a mild P-stress symptom and elevated cellular C:P and N:P ratios. Interestingly, glyphosate-grown cells showed an increased sinking rate, suggesting that glyphosate as the sole P source might enhance the efficiency of C export by E. huxleyi, which would compensate for the expected decline in primary productivity (and hence carbon efflux) in the future more nutrient-depleted ocean. This biogeochemical implication needs to be further studied and verified, however.

Phosphorus Cycle and Primary Productivity Changes in the Tethys Ocean During the Permian-Triassic Transition: Starving Marine Ecosystems

The ultimate cause(s) of the end-Permian mass extinction (∼252 Ma ago) has been disputed. A complex interplay of various effects, rather than a single, universal killing mechanism, were most likely involved. Climate warming as consequence of greenhouse gas emissions by contemporaneous Siberian Traps volcanism is widely accepted as an initial trigger. Synergetic effects of global warming include increasing stratification of the oceans, inefficient water column mixing, and eventually low marine primary productivity culminating in a series of consequences for higher trophic levels. To explore this scenario in the context of the end-Permian mass extinction, we investigated sedimentary total organic carbon, phosphorus speciation as well as nickel concentrations in two low-latitude Tethyan carbonate sections spanning the Permian-Triassic transition. Total organic carbon, reactive phosphorus and nickel concentrations all decrease in the latest Permian and are low during the Early Triassic, pointing to a decline in primary productivity within the Tethyan realm. We suggest that the productivity collapse started in the upper C. yini conodont Zone, approximately 30 ka prior to the main marine extinction interval. Reduced primary productivity would have resulted in food shortage and thus may serve as explanation for pre-mass extinction perturbations among marine heterotrophic organisms.

How to make regenerative practices work on the farm: A modelling framework

CONTEXTWell-managed agricultural land can provide ecosystem services and contribute positively to the environment. Many of these services are mediated through the soil and are referred to as soil functions. Regenerative agriculture is a mode of agriculture that uses soil conservation as the entry point to regenerate and contribute to these ecosystem services, with the aspiration that this will enhance not only environmental, but also social and economic dimensions of food production. OBJECTIVEThe main objective of this paper is to create a modelling framework which allows the ex-ante redesign of diverse farming systems and assessment of ecosystem services associated with regenerative agriculture in diverse pedo-climatic conditions. METHODSWithin this modelling framework we combined two models (Soil Navigator (SN) and FarmDESIGN (FD)) to consider soil attributes at the field-scale and environmental and socio-economic outcomes at farm-scale. We used a Dutch dairy-farm as case-study to demonstrate how this framework can be used to assess associated ecosystem services and explore alternative farm configurations. RESULTS AND CONCLUSIONSCombining SN with FD indicated what ecosystem services could be improved in a local context. Together these models help to evaluate the impact of soil management practices as the basis for exploring the overall socio-economic and environmental sustainability of our dairy case-study farm. For our dairy case-study farm, we found a set of management practices that delivered four out of the five functions at a high capacity, at the expense of primary productivity (from high to medium) and farm profitability (from 55,620 to 40,720 € yr−1). The decline in primary productivity, however, causes an improvement in other ecosystem services such as, climate regulation (increased from medium to high) and the soil organic matter surplus (increased with 7%). While this study successfully demonstrated an initial combination of SN and FD models for the ex-ante redesign and assessment of farming systems towards regenerative agriculture, further model development is essential to widen the applicability of this study to include emerging farming practices and new indicators of sustainability that are measured over a longer period. SIGNIFICANCEFor regenerative agriculture to be meaningful for diverse farming systems, we need methods that give insight into the efficacy of regenerative management to meet multiple ecosystem services within local contexts. As such, our modelling framework can be used by researchers as a tool to help various stakeholders to assess and redesign farms based on the objectives of regenerative agriculture.

Did selection for seed traits across the Cretaceous/Paleogene boundary sort plants based on ploidy?

Paleobotanists debate whether the Cretaceous/Paleogene boundary (KPB) event was selective. As the hypothesis that the KPB event selected for plants with fast-return leaf economic traits (e.g. deciduousness) has lost empirical support in recent investigations, researchers have turned to alternative hypotheses to explain an abrupt decline in primary productivity across the KPB. Two contemporary hypotheses designed to explain selectivity among plants across the KPB are that (1) polyploids exhibited greater survivorship than their diploid progenitors or counterparts (i.e. the KPB-whole genome duplication or WGD hypothesis) and that (2) plants with desiccation-tolerant (DT), i.e. orthodox, seeds exhibited greater survivorship than plants with desiccationsensitive (DS), also known as recalcitrant, seeds. Late embryogenesis abundant (LEA) protein gene families are perceived to confer DT and seed longevity among vascular plants. Non-parametric Wilcoxon signed-rank test for matched pairs and a Mann-Whitney U test reveal that plant lineages perceived to have undergone WGD across the KPB exhibit significantly greater numbers of LEA genes than those that did not. On the basis of these data, this investigation elicits a merger between the KPB-WGD and KPB-seed traits concepts. However, emphasis is shifted from the concept of WGD as an immediate adaptation to climatic stress at the KPB (the KPB-WGD hypothesis) to the concept that WGD was an exaptation, which, by definition, fortuitously enhanced the survival of vascular plants across the KPB but that probably evolved initially in other climatic contexts.

Oceanic primary production decline halved in eddy-resolving simulations of global warming

Abstract. The decline in ocean primary production is one of the most alarming consequences of anthropogenic climate change. This decline could indeed lead to a decrease in marine biomass and fish catch, as highlighted by recent policy-relevant reports. Because of computational constraints, current Earth system models used to project ocean primary production under global warming scenarios have to parameterize flows occurring below the resolution of their computational grid (typically 1∘). To overcome these computational constraints, we use an ocean biogeochemical model in an idealized configuration representing a mid-latitude double-gyre circulation and perform global warming simulations under an increasing horizontal resolution (from 1 to 1/27∘) and under a large range of parameter values for the eddy parameterization employed in the coarse-resolution configuration. In line with projections from Earth system models, all our simulations project a marked decline in net primary production in response to the global warming forcing. Whereas this decline is only weakly sensitive to the eddy parameters in the eddy-parameterized coarse 1∘ resolution simulations, the simulated decline in primary production in the subpolar gyre is halved at the finest eddy-resolving resolution (−12 % at 1/27∘ vs. −26 % at 1∘) at the end of the 70-year-long global warming simulations. This difference stems from the high sensitivity of the sub-surface nutrient transport to model resolution. Although being only one piece of a much broader and more complicated response of the ocean to climate change, our results call for improved representation of the role of eddies in nutrient transport below the seasonal mixed layer to better constrain the future evolution of marine biomass and fish catch potential.

Observed Global Increases in Tropical Cyclone‐Induced Ocean Cooling and Primary Production

AbstractTropical cyclones provide an important source of ocean mixing, bringing cold, nutrient‐rich water to the surface and triggering phytoplankton blooms. Here, we show significant increases in global tropical cyclone‐induced sea surface temperature cooling and surface chlorophyll‐a concentration of 0.05°C and 3.7 × 10−3 mg m−3 per decade over the past 20–35 years. The trends have been driven primarily by an increase in the intensity of strong tropical cyclones. The increase in chlorophyll‐a concentration has been, on average, 1.6% per decade in oligotrophic areas during the tropical cyclone season, in contrast to a decrease of 0.1% per decade during the other months. This tropical cyclone‐induced increase has partially mitigated the overall decline in primary production under climate change.

Has primary production declined in the Salish Sea?

Declining primary production has been proposed as an explanation for the declines in coho (Oncorhynchus kisutch) and Chinook (Oncorhynchus tshawytscha) salmon in the Salish Sea since the 1970s. Marine sediments maintain a continuous record of conditions in the overlying water. We used stable isotopes of organic carbon and nitrogen measured in 21 sediment cores to determine the contributions and fluxes of marine-derived and terrigenous organic matter over time. The flux of marine-derived organic matter shows no trend for at least the last 100 years. An apparent increase in the marine flux in recent years is due to remineralization of organic matter as it passes through surface sediments. In contrast, the flux of terrigenous organic matter has increased over the last century in the Strait of Georgia, while in Puget Sound, terrigenous flux peaked in the mid-20th century. Total primary production has neither increased nor decreased in the Salish Sea over the last century. Consequently, a decline in primary production cannot explain recent declines in fish populations.

The Contribution of Small Phytoplankton Communities to the Total Dissolved Inorganic Nitrogen Assimilation Rates in the East/Japan Sea: An Experimental Evaluation

As a part of Korean-Russian joint expeditions in the East/Japan Sea during 2012 and 2015, a set of total and small (<2 μm) phytoplankton NO3− and NH4+ uptake rate estimations were carried out. The study aimed to assess the spatio-temporal variations in dissolved inorganic nitrogen (DIN) assimilation by the total and small phytoplankton. The results show that the total NO3− uptake rates during 2012 varied between 0.001 and 0.150 μmol NL−1h−1 (mean ± SD = 0.034 ± 0.033) and that the total NH4+ uptake rates ranged between 0.002 and 0.707 μmol NL−1h−1 (mean ± SD = 0.200 ± 0.158). The total uptake rates during 2015 were ranged from 0.003 to 0.530 (mean ± S.D. = 0.117 ± 0.120 μmol NL−1h−1) for NO3− and from 0.008 to 1.17 (mean ± S.D. = 0.199 ± 0.266 NL−1h−1) for NH4+. The small phytoplankton NO3− and NH4+ uptake rates during 2015 ranged between 0.001 and 0.164 (mean ± S.D. = 0.033 ± 0.036) μmol NL−1h−1 and 0.010–0.304 (mean ± S.D. = 0.101 ± 0.073) μmol NL−1h−1, respectively. Small phytoplankton’s contribution to the total depth-integrated NO3− and NH4+ uptake rates ranged from 10.24 to 59.36% and from 30.21 to 68.55%, respectively. The significant negative relationship observed between the depth-integrated total NO3− and NH4+ uptake rates and small phytoplankton contributions indicates a possible decline in the DIN assimilation rates under small phytoplankton dominance. The results from the present study highlight the possibility of a reduction in the total DIN assimilation process in the East/Japan Sea when small phytoplankton dominate under strong thermal stratification due to sea surface warming. The present study’s findings agree with the model projections, which suggested a decline in primary production in the global warming scenario.

Vegetation structural change and CO2 fertilization more than offset gross primary production decline caused by reduced solar radiation in China

Terrestrial gross primary production (GPP) is the largest carbon flux from the atmosphere to the terrestrial ecosystems. However, how GPP dynamics respond to vegetation structural change (VSC), climate change, and rising CO2 concentration are still unclear. In this study, we developed a process-based model (i.e., Farquhar GPP Model) to characterize GPP dynamics in China from 2001 to 2016, and further identify the dominant drivers for GPP variation related to VSC, climate change, and rising atmospheric CO2 through model scenario design. During the study period, VSC showed an overwhelmingly positive impact on annual total GPP (i.e., 39.2 Tg C yr−1, P<0.001), followed by the fertilization effect of rising CO2 (i.e., 11.9 Tg C yr−1, P<0.001). However, climate variation would be expected to have an overall negative effect (i.e., -9.9 Tg C yr−1, P<0.001), which is primarily related to the decline of the incoming solar radiation over this period. Consequently, China's GPP showed a remarkable upward trend (i.e., 40.5 Tg C yr−1, P<0.001) during the study period. Our study highlighted the strong positive GPP contribution from VSC, which is mainly related to forest increase under the background of forest cover changes primarily from widespread forest conservation and restoration programs implemented in China since the late 1990s. Therefore, our study suggests that forest conservation and restoration could effectively increase terrestrial ecosystem GPP, despite the negative effects of climate change.

Twenty-first century ocean warming, acidification, deoxygenation, and upper-ocean nutrient and primary production decline from CMIP6 model projections

Abstract. Anthropogenic climate change is projected to lead to ocean warming, acidification, deoxygenation, reductions in near-surface nutrients, and changes to primary production, all of which are expected to affect marine ecosystems. Here we assess projections of these drivers of environmental change over the twenty-first century from Earth system models (ESMs) participating in the Coupled Model Intercomparison Project Phase 6 (CMIP6) that were forced under the CMIP6 Shared Socioeconomic Pathways (SSPs). Projections are compared to those from the previous generation (CMIP5) forced under the Representative Concentration Pathways (RCPs). A total of 10 CMIP5 and 13 CMIP6 models are used in the two multi-model ensembles. Under the high-emission scenario SSP5-8.5, the multi-model global mean change (2080–2099 mean values relative to 1870–1899) ± the inter-model SD in sea surface temperature, surface pH, subsurface (100–600 m) oxygen concentration, euphotic (0–100 m) nitrate concentration, and depth-integrated primary production is +3.47±0.78 ∘C, -0.44±0.005, -13.27±5.28, -1.06±0.45 mmol m−3 and -2.99±9.11 %, respectively. Under the low-emission, high-mitigation scenario SSP1-2.6, the corresponding global changes are +1.42±0.32 ∘C, -0.16±0.002, -6.36±2.92, -0.52±0.23 mmol m−3, and -0.56±4.12 %. Projected exposure of the marine ecosystem to these drivers of ocean change depends largely on the extent of future emissions, consistent with previous studies. The ESMs in CMIP6 generally project greater warming, acidification, deoxygenation, and nitrate reductions but lesser primary production declines than those from CMIP5 under comparable radiative forcing. The increased projected ocean warming results from a general increase in the climate sensitivity of CMIP6 models relative to those of CMIP5. This enhanced warming increases upper-ocean stratification in CMIP6 projections, which contributes to greater reductions in upper-ocean nitrate and subsurface oxygen ventilation. The greater surface acidification in CMIP6 is primarily a consequence of the SSPs having higher associated atmospheric CO2 concentrations than their RCP analogues for the same radiative forcing. We find no consistent reduction in inter-model uncertainties, and even an increase in net primary production inter-model uncertainties in CMIP6, as compared to CMIP5.

Global ocean primary production trends in the modern ocean color satellite record (1998–2015)

Ocean primary production (PP), representing the uptake of inorganic carbon through photosynthesis, supports marine life and affects carbon exchange with the atmosphere. It is difficult to ascertain its magnitude, variability, and trends due to our inability to measure it directly at large scales. Yet it is paramount for understanding changes in marine health, fisheries, and the global carbon cycle. Using assimilation of ocean color satellite data into an ocean biogeochemical model, we estimate that global net ocean PP has experienced a small but significant decline −0.8 PgC y−1 (−2.1%) decade−1 (P < 0.05) in the 18-year satellite record from 1998 to 2015. This decline is associated with shallowing surface mixed layer depth (−2.4% decade−1) and decreasing nitrate concentrations (−3.2% decade−1). Relative contributions to PP by various types of ocean phytoplankton have changed, with decreases in production by intermediate-sized phytoplankton represented by chlorophytes (−14.3% decade−1). This is partially compensated by increases from the unique, more nutrient-efficient, coccolithophores (8.4% decade−1). Geographically, the North and Equatorial Indian Oceans are responsible for much of the decline in PP, falling 0.16 and 0.69 PgC y−1 decade−1, respectively. Reduced production by large, fast-growing diatoms along with chlorophytes characterizes the decline here. In contrast, increases in PP are found in the North and North Central Pacific. The increases here are led by chlorophytes in the North Pacific and the small cyanobacteria in the North Central Pacific. These results suggest that the multi-decadal satellite observational record, coupled with an underlying representation of marine biodiversity in a model, can monitor the uptake of carbon by phytoplankton and that changes, although small, are occurring in the global oceans.